1. Field of the Invention
The present invention generally relates to the field of remote continuing discrete monitoring of particular substances, and more particularly to a apparatus for the sensing of gases in harsh environments such as, but not limited to, hydrogen sulfide gas on a continuing discrete basis, and the communication of that information remotely. It also relates to the method of operation of that apparatus.
2. Description of the Prior Art
Exposure to hazardous gases in confined spaces has been recognized as a major danger for many years for both personnel required to enter such spaces and the damaging effect the gases have on the equipment and materials exposed to the gases and their chemical byproducts. The latter condition is generally referred to herein as a harsh environment.
Many devices have been developed to indicate the level of hazardous gases for the protection of individuals and equipment but they all have several serious drawbacks. The present invention is designed to eliminate these drawbacks and to provide an apparatus that can remain in place without suffering the damaging effects of the harsh environment in which it is suspended.
Prior art sensing devices (the sensors) for the detection of hydrogen sulfide gas cannot ordinarily be continuously exposed to the gas or they will become saturated and loose the ability to function. This problem accounts for the need to have the prior art sensor devices located external to the gas environment, have a sampling tube with a pump mechanism to pump the atmosphere to be tested to the sensor, and then after the reading is made the sensor must be “aired out” to prevent saturation. This configuration limits the placement of prior art instruments to secure locations and the availability of power. Prior art comprising portable, hand held devices used for personal safety are limited to the lower limits of potential gas concentrations and are not capable of remaining in the sensing environment for long periods of time.
Examples of the prior art follow. The first is Wright, et al, U.S. Pat. No. 5,981,289 for a hydrogen sulfide analyzer that continuously samples waste water from a waste stream or reservoir and measures the concentration of purgeable hydrogen sulfide present. This information, when combined with the volume of water present, provides a control quality signal that regulates the feed rate of a destructor chemical into a waste stream. This results in chemical savings for the user. A second result is the reduction in odor complaints and the corrosion problems associated with hydrogen sulfide emissions. The analyzer measures only the purgeable hydrogen sulfide contained in the liquid sample. The analyzer violently agitates the sample containing dissolved hydrogen sulfide in solution to simulate actual conditions at points of agitation in the waste water stream. It also provides nearly optimal partial pressure conditions for the hydrogen sulfide to exit the solution as a free gas. Any hydrogen sulfide that does not come out of solution in the analyzer is not of interest to the user since it will most likely not come out of solution in the treatment process either. The analyzer controls the feed of the destructor chemical based upon the measured quantity and concentration of hydrogen sulfide that is likely to come out of solution in the collection/treatment process. It does not measure the total amount of sulfides present as other analyzers do. This is an important feature since it is wasteful to treat a condition that is not going to be a problem.
While Wright teaches a method of using a hydrogen sulfide sensor to determine the amount of a “destructor chemical” that should be released into an environment to mitigate the effect of the hydrogen sulfide, it does not address the problem of the continuous sampling's effect on the sensor's efficacy. The present invention improves this method by using clean air to purge the sensor, as well as has the ability to measure the amount of hydrogen sulfide in a gas, rather than in a liquid.
The next reference of interest is Church et al., U.S. Pat. No. 6,198,400 concerning portable gas detection and/or monitoring apparatus for a hostile environment. It includes a case having a substantially cylindrical wall and two opposite end caps sealably connected to the cylindrical wall, at least one of the end caps being removable from the cylindrical wall, and at least a portion of the cylindrical wall being transparent. A gas detection and/or monitoring unit is mounted in the case and includes gas-sensing means in sealed fluid communication with the ambient atmosphere outside the case. Data processing means is operatively connected to the gas sensing means, and data storage means and information display means is operatively connected to the data processing means. Calibrating means is operatively connected to the data processing means for calibration thereof to a predetermined gas concentration measured by the gas sensing means, the calibrating means including external switching means for selectively connecting the data processing means to the data storage means to allow transfer of data from said data storage means to said data processing means. Communication means is operatively connected to the data processing means or the data storage means for communicating data to the data processing means or the data storage means to an external destination and/or vice versa. A power supply is mounted in the case and operatively connected to the gas detection and/or monitoring unit and/or the gas sensing means.
Church teaches a suspension method for placing a sensing device in a hazardous environment, but it does not solve the problem of the saturation of the sensing device that renders it useless in a relatively short amount of time when placed in such a hazardous environment. The instant invention improves upon this teaching by solving the problem of saturation, by allowing the hazardous substance to only flow across the sensor membrane for a given amount of time and then flushing the membrane clean of detrimental particles. The present invention also does not include a housing having a transparent wall portion, and its switching means are internal, not external.
A further reference is Li, et al., U.S. Pat. No. 5,425,268 for water immersible vapor sensor. A continuous vapor sensor is disposed within a partially open protective enclosure which restricts (but does not exclude) the entry of liquid and means for excluding liquid from a portion of the enclosure, such as a non-wetting attachment material. The assembly allows the use of a continuous sensor which is adversely impacted by liquid contact in locations where the assembly may be immersed. The enclosure traps a sufficient amount of vapor to maintain a minimum vapor volume when the enclosure is submerged to a significant depth below a water level. The means for excluding controls the location of the minimum vapor volume to protect the sensor.
Li teaches that a sensor can be assembled to measure continuously vapor concentrations by drawing the vapor across the sensor. It is also taught that the sensor can communicate with an external recording device; however, the faults of such a system are highlighted in a hazardous environment, in which continuously exposed sensor equipment becomes desensitized, drastically reducing its efficacy and reliability. The instant invention fixes this problem by drawing in only the amount of sample necessary to take an accurate reading, and then purging the sensor of the harmful substance with clean air. Additionally, traditional means of communication with external devices are unable to operate when placed in hazardous environments such as in manholes.
Another reference is Novack, et al, U.S. Pat. No. 4,664,886 for a trimode gas detection instrument having three operating modes, one which monitors the level of combustible gases, a second which monitors oxygen, and a third which monitors the displacement of air by an unknown gas. Only two sensors are used, a combustible gas sensor and an oxygen sensor. A switch selects the input to a readout so that the user can quickly observe the concentration readings in any of the three modes. In the depletion mode the readout is calibrated in relation to the inverse of the normal concentration of oxygen in air, i.e., zero depletion corresponds to an oxygen concentration of 21%. In the event that an unknown gas displaces air in a sample atmosphere, concentration of the unknown gas appears on the readout, such that zero oxygen corresponds to a concentration of 100% unknown gas.
Novak teaches the use of a gas detection system that has three operating modes; each mode is initiated by an electronic method, through the use of a switch. The instant invention simplifies and improves upon Novak's concept by using a mechanical means to switch between positions on a three position valve, which is used to solve the sensor saturation problem previously described. Novak does not address the saturation of the sensor problem. The present invention's use of a mechanical method overcomes the problems caused by use in a hazardous or corrosive environment on electronic components. The present invention also solves the problem of using multiple sensors by employing just one sensor for gas detection.
An additional reference is Bell, et al., U.S. Pat. No. 5,010,021 concerning a method for restoring the sensing capacity of an electrical sensor. A selected component of a fluid mixture, for example a reduced sulfur compound vapor in air, is detected by selectively adsorbing the component onto a conductive thin layer of material having a chemical affinity for such component and observing the resultant change of electrical resistivity of the layer. The sensitivity of the detector changes with accumulation of the component on the sensor. The accumulation of the component on the sensor is removed by oxidizing and evolving the component from the sensor to restore the sensor to a linear operating region. The accumulated component is preferably oxidized by reacting the component with ozone. The dynamic range of the sensor is increased by counteracting the tendency for the component to accumulate by continuously feeding back ozone to or controlling the temperature of the sensor so that the sensor operates in a linear region near null.
Bell teaches a method for cleaning a sensor between testing through the use of oxidation. This method has the drawback that it uses a chemical means to decontaminate the sensor. The present invention uses a conditioned air source for decontamination, a preferred method compared to Bell due to the chemistry of the sensing device.
A final reference is Worth, et al, U.S. Design Pat. No. 432,037. It teaches the ornamental design for a gas detection unit which is cylindrical in shape. The present invention has rectilinear shape.